Means and method for detecting three-way call attempts

ABSTRACT

Method, including monitoring an audio signal on a telephone line with a detector and detecting an energy pulse in the audio signal on the telephone line; processing the energy pulse with a processor, where the energy pulse comprises a plurality of frequency components; determining a length of the energy pulse on the telephone line; calculating a phase for each of the plurality of frequency components to generate a plurality of phase values; generating a signal if the plurality of phase values are linear and if the length of the energy pulse is less than 40 milliseconds, where the signal is indicative that the plurality of phase values are linear and that the length of the energy pulse is less than 40 milliseconds, and further indicative that the signal is a three-way call attempt on the telephone line; and transmitting the signal to a host computer.

FIELD OF THE INVENTION

The present invention relates generally to the field of detectingthree-way call attempts in controlled telecommunications systems. Inparticular, the invention relates to a system and method for detecting apulse of energy having components with a common phase delay. Accordingto the present invention, a pulse with this characteristic is indicativeof a three-way call attempt. The present invention preferably computesthe Fast Fourier Transform (FFT) to calculate the phases of thecomponents that comprise the pulse.

BACKGROUND OF THE INVENTION

Many institutions, such as prisons, nursing homes, mental institutions,etc., include controlled telecommunications systems that offer inmatesor residents limited calling access. One reason for controlling use ofthe system is to prevent the institution from incurring unaccountabletelephone costs. Other reasons for controlling access to the systeminclude preventing harassing calls to outside parties, preventingfraudulent activities, etc. Therefore, systems in such environmentsoften monitor and control the telephone activity of each inmate orresident. For example, systems may restrict calling to only certaintelephone numbers. Systems may also have a means of maintaining callrecords for each inmate or resident, and a means for communicating withcalled parties to enable the called parties to prevent future telephonecalls from inmates or residents. In short, the communications systemused in a regulated institution must employ unique monitoring andcontrol functions often unnecessary in other types of telecommunicationssystems.

In order for the methods of monitoring and control to be effective, itis important to prevent inmates or residents from exploiting anyloop-holes that can be used to bypass the control features of thesystem. For example, inmates or residents have been known to usethree-way calling to have an outside party connect the inmate orresident to a blocked number. A three-way call is initiated when theremote called party depresses the hook switch on the telephone,generating a hook flash signal. The caller is temporarily put on holdwhile the called party establishes a connection with a third party.Then, all three parties can converse. Using three-way calling, theinmate or resident may utilize the institution's call system to, amongother things, access blocked telephone numbers, for example, toperpetrate additional criminal activities, or harass certain parties.

It is therefore critical to carefully monitor all outgoing telephonecalls for three-way call attempts. Without such monitoring, many of thesystem's control features of a telecommunications system can be renderedineffective. Currently, there are systems and methods known in the artfor detecting three-way call attempts. Many of these systems however,are inaccurate and subject to both false positives and false negatives.Also, many of these systems are effective only in certain types oftelecommunications systems.

For example, one such system known in the art for detecting three-waycall attempts monitors for pulses of energy indicative of a hook-flashby detecting the frequency of the energy pulse to determine if it ischaracteristic of a hook-flash (i.e., a three-way call attempt).Specifically, the system includes a low pass filter for passing energysignals having frequencies below 500 Hertz (“Hz”), preferably in therange of 100 to 300 Hz, and an energy detector for detecting specificelectrical energy pulses passing through the filter and having apredetermined minimum magnitude. The system also includes a softwarewindow analyzer, which cooperates with the energy detector to detectspecific events, such as sound, occurring on the telephone line during apredetermined time window after the detection of the aforementionedenergy pulse. The software window analyzer includes a timer means thatis activated by the detection of the energy pulse, and a sound means fordetecting the occurrence of sound on the telephone line during at leastone of multiple windows of time defined by the timer means. Thenon-occurrence of sound on the telephone line during a specified timewindow is used by the system to confirm that the detected energy pulseis in fact a three-way call attempt. A counter means is furtherimplemented for counting specific energy pulses detected by the energydetector during the time window when the remote party is using apulse-dial telephone. This system, by simply monitoring for a pulsecomposed of certain frequencies, is often inaccurate and cannot operatein digital systems.

A similar system is also designed to detect the presence of an energypulse indicative of a hook-flash. Specifically, the system is designedto detect a pulse that is comprised of frequency components below 500 Hzand above a predetermined threshold. The existence of the hook-flash isconfirmed by digital signal processing equipment which identifies arapid drop-off in energy, which is indicative of a hook-flash signal.Optionally, the hook-flash may be further confirmed by includingsoftware for cooperating with the energy detector to ascertain whethersound has occurred in the telecommunication during a predeterminedperiod following the first hook-flash signal.

Still another known system includes three-way call detection circuitthat uses digital signal processing to identify a third partyconnection. The system operates by establishing a baseline backgroundnoise. The system identifies a drop in noise level below the establishedbaseline background noise as an indication that a three-way conferencecall has been attempted by the called and/or calling party.

Yet another known system monitors all connected telephone lines forindicia representative of a three-way call attempt. For example, thesystem may monitor for a digital PCM signal or a period of silence,followed by a release pulse, followed by yet another period of silence.Upon detection of a possible three-way call attempt, the three-way calldetection circuit examines the digital signals to determine the spectralcharacteristics (i.e., time duration, frequency, and energy level) of asuspected release pulse of the suspected three-way call attempt. Thesystem utilizes pattern recognition techniques to compare the suspectedrelease pulse with a reference release pulse indicative of a three-waycall attempt. The system also monitors for periods of silence before andafter the suspected release pulse. If the system finds that thesuspected release pulse is substantially similar to the referencerelease pulse and that the correct periods of silence surrounding thesuspected release pulse are present, the system responds to thedetection, for example, by disconnecting the telephone call, playing arecording, or creating a record of the three-way call attempt.

Yet another known system for detecting three-way calls monitors audiosignals for features that distinguish voice and line-generated audiosignals from audio signals produced by events associated with three-waycall attempts. The distinguishing features used are pulse patterns thatare strongly correlated with either audio signals generated by centraloffice switching activity (‘clicks’) (reference features) orvoice-generated audio signals (reset features). Audio signals arecontinuously monitored for reference and reset features over selectedintervals or sampling windows. Sampling windows are reset whenever resetfeatures are detected in the associated audio signal segment. Audiosignals that are free of reset features and include reference featuresare tagged as potential click events. A three-way call event is declaredwhen audio signals associated with consecutive sample windows are taggedas potential three-way call events. In this system, a control programsamples the audio signal at the selected rate and sorts the sampledsignals during a sampling window to produce a profile of the sampledaudio signal. The profile comprises counters for tracking the number,strength (loudness), and separation of signal pulses. These counters maybe compared in various combinations with counter values extracted fromvoice-generated audio signals (reset thresholds) and three-way callgenerated audio signals (reference thresholds) to declare a three-waycall attempt, continue sampling, or reset the sampling window.

Another known system counts signal characteristics to detect three-waycall attempts. The system samples audio from a telephone conversation,sorts the sampled signals into a profile of levels for the sampled audiosignals, and monitors the profile of sampled audio signals for reset andreference conditions. In this system a reset condition is a pulsepattern inconsistent with patterns generated by three-way call events.Reference conditions, in contrast, are pulse patterns identified fromsampled audio signals that are consistent with patterns generated bythree-way call events. If a reference condition is detected, thetelephone call is tagged as having a possible three-way call attempt.The system concludes that a three-way call attempt has occurred when twoconsecutive tags have been made to the same telephone call.

Still another known system detects three-way calls by recognizing thateach telephone connection has a characteristic reflection, or echo,idiosyncratic to that connection. The echo characteristics of aparticular telephone connection are altered, for example, when athree-way calling feature is activated by the remote party at theoriginal destination thereby adding a third party at a secondarydestination. The system includes means for “zeroing out” or cancelingthe characteristic echo once a connection has been established by usingan adaptive finite impulse response (FIR) filter. The system alsoincludes response means for implementing a predetermined response whenan undesirable event is detected. Examples of the responses which can bepre-programmed include call termination, playing a prerecorded message,generating a tone which may be heard by one or more parties to the call,muting the microphone of the local telephone and recording the date andtime of the remote party's attempt to initiate the three-way call.

Other systems are known which incorporate methods of monitoring calls intelecommunications management systems. For example, the methods includemeans for detecting tones commonly associated with call bridging andcall forwarding attempts. One such method is directed to the detectionof tones such as ring signals, busy signals, special information tones(“SIT tones”), dual tone multi-frequency tones (“DTMF”), call progresstones or other similar tones characteristic of the placement of atelephone call.

In view of the foregoing, a need clearly exists for an improved methodand system of three-way call detection capable of more accuratelydetecting three-way call attempts in analog and digitaltelecommunications systems. Existing methods and systems are exceedinglyinaccurate resulting in far too many false positive and false negativedetections. The three-way call detection system of the invention detectsthree-way call attempts by analyzing the communications path between theoriginator and recipient in a telecommunications network. The system ismore accurate than existing systems and searches for pulses havingcharacteristics consistent with a three-way call without the need todetect the frequency of an energy pulse.

SUMMARY OF THE INVENTION

The present invention embodies three-way call detection circuit for usewith an existing telephone management system, and is designed to reducethe number of three-way call attempts not detected by current three-waycall detection techniques as well as eliminate or significantly reducethe number of false three-way calls detected. The system of the presentinvention may be implemented in a variety of facilities including, butnot limited to, penal institutions, mental institutions, nursing homes,rehabilitation centers, correctional facilities, government agencies,private and public business, and the like.

Typically, a telephone management system used by such facilitiesconsists of a multitude of telephones connected to a switchboard device.The switchboard device routes calls, performs voice prompts, andresponds to menu selections. Telephone calls placed by users of thetelephone management system are routed through the switchboard deviceand connected to the proper outgoing trunk based on the type of callplaced (e.g., collect, debit, etc.). An integrated cross point switchenables any telephone to access any available outgoing trunk.

The three-way call detection circuit of the present invention isutilized each time a telephone call is placed by a user of the telephonemanagement system. The circuit constantly monitors all active trunklines and telephone conversations. During a telephone call, thethree-way call detection circuit monitors the connection for pulses ofenergy associated with the act of the called party initiating athree-way call. Specifically, the system of the present inventionmonitors for the presence of audio signals generated by central officeswitching activity (hereinafter, “clicks”) indicative of a three-waycall initiation attempts.

For a called party to initiate a three-way call, the called partytypically depresses the hook-switch momentarily to put the calling partyon hold and to call a third-party. The called party's depression of thehook-switch generates a hook-flash signal, which results in the centraloffice generating a click on the inmate's telephone line. The click ismost generally a pulse of energy with certain known characteristics.Therefore, by monitoring for pulses of energy with characteristicsconsistent with a click, three-way calls can be identified. Anappropriate response (terminating the telephone call, monitoring thetelephone call, warning the called party, etc.) can then be initiated.As discussed above, there are several known methods and systems fordetermining if a three-way call attempt has been made.

The present invention provides an improved method of monitoring for sucha click. According to the present invention, a pulse is a clickindicative of a three-way call attempt if the phases of the frequencycomponents that comprise the pulse have a common group delay (i.e., eachcomponent has the same, or approximately the same phase delay). A clickis comprised of many components all of which are generated at nearly thesame instant in time. Thus, in accordance with the present invention,any of the components that comprise the pulse can be analyzed todetermine if the pulse is indicative of a three-way call click (i.e.,the invention does not require the filtering or analysis of one specificband or range of frequencies).

To analyze a pulse that may be indicative of a three-way call, the FFTis applied to the pulse to convert it into the frequency domain. As isknown in the art, the FFT is a computationally efficient mathematicaltechnique that converts digital information from the time domain to thefrequency domain for rapid spectral analysis. Specifically, the FFT isan algorithmic optimization of the discrete Fourier transform (“DFT”)(i.e., the FFT produces the same results as the DFT but using far fewercomputations). Therefore, although the DFT is discussed by way ofbackground below, this discussion applies equally to the FFT.

The DFT breaks down a digital signal into its frequency components(i.e., into a summation of harmonically-related cosine and sine waves).For a discrete (i.e., digital) signal, x[t], with N samples, the DFT isdefined as:

$\begin{matrix}{{{X\left\lbrack w_{k} \right\rbrack} = {\sum\limits_{n = 0}^{N - 1}{{x\left\lbrack t_{n} \right\rbrack}{\mathbb{e}}^{{- j}\; w_{k}t_{n}}}}},{k = 0},1,2,\ldots\mspace{11mu},{N - 1}} & (1)\end{matrix}$

In this equation (1), x[t_(n)] is the signal in the time domain, t_(n)is the n_(th) sampling instant, W_(k) is the k_(th) frequency sample(i.e., the k_(th) frequency component), and X[w_(k)] is the DFT of thesignal. The DFT computes a complex coefficient for each frequencycomponent that comprises the signal. As is known in the art, e^(−jw)^(k) ^(t) ^(n) can be broken down into a cosine and sine component(i.e., e^(−jw) ^(k) ^(t) ^(n) =cos(w_(k)t_(n))+jsin(w_(k)t_(n))).Therefore, the complex coefficient is a representation of a cosine andsine wave (each with frequency w_(k)) that comprise the k_(th) frequencycomponent of the signal. The real component of the complex coefficientis the magnitude of the cosine wave, and the imaginary component of thecomplex coefficient is the magnitude of the sine wave.

The complex coefficient can also be used to calculate the overallmagnitude and phase of the corresponding component. Specifically, themagnitude (or amplitude) of the component is the square root of the sumof the squares of the real and imaginary components of the correspondingcoefficient:Magnitude=√(Real²+Imaginary²)  (2)

The phase is the arctangent of the imaginary component divided by thereal component:Phase=atan(Imaginary/Real)  (3)

Therefore, a cosine wave corresponds to a wave with 0 degrees phase (0radians) and a sine with corresponds to a wave with 90 degrees phase(π/2 radians). The range of possible phase values that can be computedby the FFT extends from −180 degrees (−π radians) to 180 degrees (nradians).

In sum, using the mathematical properties of the DFT (or the FFT), themagnitude and phase for each component that comprises a digital signalcan be developed. In the system of the present invention, the FFT isused to calculate the phases of the components that comprise the pulse.

After the phases are calculated for each of the frequency componentsthat comprise a pulse, the phase data is analyzed to determine if thepulse is a click indicative of a three-way call attempt. As is known inthe art, if a called party attempts to initiate a three-way call,central office switching activity (i.e., a three-way call click) isgenerated on the telephone line of the calling party. This click, orpulse of energy, is comprised of many components. Importantly, becausethe waves (i.e., the frequency components that comprise the pulse) arecreated at close to the same instant in time, the phase delay for eachof the components that comprise the pulse should be approximately thesame. As will be discussed below, the phase delay can be calculated fromthe phase, and is constant across all components of the pulse if phasevaries linearly as a function of frequency.

First, the phases computed by the FFT are preferably “unwrapped” (i.e.,converted from a range of −π to π to a larger range to smooth outartifacts that result from the FFT calculation). The phase should beunwrapped because, although the FFT calculates a phase for eachcomponent, the sinusoidal nature of the output of the FFT results in acalculated phase that ranges from −π to π. If the real phase extendsbeyond this range, large jumps in phase may appear to exist betweencomponents when the calculated phrase“wraps around” the −π to π range.Therefore, phase unwrapping operates to correct these phase-jumpingartifacts by adding multiples of +/−2π when absolute jumps betweenconsecutive phases are greater than a predefined tolerance (e.g., π).The resulting unwrapped phases are thus smoother and devoid ofartificial jumps.

After the phase is unwrapped, it is analyzed for linearity. As discussedabove, and as will be developed below, if phase varies linearly as afunction of frequency, the phase delay is constant. Phase is in a unitof radians. However, the system of the present invention is used tolocate pulses of energy where each component has the same “phase delay”,which is in unit time. Specifically, phase delay, P(ω), is defined as:P(ω)=Θ(ω)/ω  (4)where Σ(ω) is the phase, or unwrapped phase, in radians of the componentof the signal having frequency ω.

As mentioned above, a click is generated by the central office and iscomposed of many frequency components. Because it is a “machinegenerated” pulse, all of the components are generated at the same timeand should therefore have a common phase delay. Thus, according to thepresent invention, if the phase delay of each component of a pulse isthe same, then the pulse is indicative of a three-way call click.

If the phase delay is constant for each component, then phase varieslinearly as a function of frequency. Therefore, as an alternative tocomputing the phase delay, the linearity of the phases, or unwrappedphases, can be calculated. If the phase is linear with respect tofrequency (i.e., Σ(ω)=α(ω), where α is a constant), then through simplesubstitution, it is evident that the phase delay will be the same (α),independent of ω. For example:P(ω)=α*ω/ω, and  (5)P(ω)=α  (6)

In the art of signal analysis, computing a “group delay”, G(ω) can beused to determine the linearity of the phase. More specifically, thegroup delay is defined as the derivative of the phase as a function offrequency:G(ω)=−d/dω(Σ(ω)).  (7)Thus, if phase is linear, the group delay will be a constant.

If the derivative is a constant (i.e., Σ(ω) is linear with respect tofrequency), then the group delay equals the phase delay (i.e., α) andthus the phase is indicative of a three-way call click. Appropriateaction can then be taken (e.g., disconnecting the call, warning thecaller, logging or recording the call, etc.).

In a preferred embodiment, the system isolates only those pulses withtime-domain characteristics that are consistent with a click, thusobviating the need to perform the computationally intensive FFT on allpulses. More specifically, the system preferably searches for only thosepulses of energy that (1) are at most 40 milliseconds (ms) in length andthat (2) are followed and preceded by a period of silence (POS). The POSthat precedes the pulse must be at least approximately 100 ms in length.The POS that follows the pulse also must be at least approximately 100ms. Of course, the time requirements can be adjusted for the specifictelecommunications system in which the three-way call detect circuit isimplemented.

If a pulse is having these characteristics is detected, then the FFT ofthe pulse signal is calculated, and the phase is analyzed as discussedabove. Of course, the system may be used with other filters andthree-way call detect methods to further increase accuracy.

Therefore, it is an object of the present invention to provide athree-way call detection method and circuit for analyzing the telephoneline of a calling party for pulses of energy having phasecharacteristics indicative of a three-way call click.

It is another object of the invention to provide a three-way calldetection method and circuit for analyzing the telephone line of acalling party for pulses of energy comprised of frequency componentshaving similar or identical phase delays.

It is still another object of the invention to provide a three-way calldetection method and circuit for analyzing the telephone line of acalling party for pulses of energy indicative of a three-way callattempt by computing the FFT of the pulses.

It is yet another object of the invention to provide a three-way calldetection method and circuit for analyzing the telephone line of acalling party for pulses of energy with time domain characteristicsconsistent with a three-way call click.

It is a further object of the invention to provide a three-way calldetection method and circuit that is not restricted to analyzing acertain band or range of frequencies.

Furthermore, it is an object of the invention to accurately detectthree-way call attempts and respond with a designated action (e.g.,disconnect, flag, record, monitor, etc.).

It is another object of the invention to provide a three-way calldetection method and circuit which stores all detected three-way callattempts in a central database.

It is still a further object of the invention to provide a three-waycall detection method and circuit capable of monitoring a telephoneconversation from the called party's side of the connection.

Additionally, it is an object of the invention to provide a three-waycall detection method and circuit which is compatible with pre-existingtelephone management systems.

Finally, it is a further object of the invention to provide a three-waycall detection method and circuit compatible with both analog anddigital telecommunications systems.

Other objects, features, and characteristics of the present invention,as well as the methods of operation and functions of the relatedelements of the structure, and the combination of parts and economies ofmanufacture, will become more apparent upon consideration of thefollowing detailed description with reference to the accompanyingdrawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the present invention can be obtained byreference to a preferred embodiment set forth in the illustrations ofthe accompanying drawings. Although the illustrated embodiment is merelyexemplary of systems for carrying out the present invention, both theorganization and method of operation of the invention, in general,together with further objectives and advantages thereof, may be moreeasily understood by reference to the drawings and the followingdescription. The drawings are not intended to limit the scope of thisinvention, which is set forth with particularity in the claims asappended or as subsequently amended, but merely to clarify and exemplifythe invention.

For a more complete understanding of the present invention, reference isnow made to the following drawings in which:

FIG. 1 shows a block diagram of the preferred configuration of thethree-way call detection system according to the present invention.

FIG. 2 depicts a schematic representation of the preferred embodiment ofthe three-way call detection circuit shown in FIG. 1 illustrating itsports and internal structure.

FIG. 3 is a schematic diagram of the preferred embodiment of the circuitused to detect energy pulses having amplitudes and durationscharacteristic of a three-way call click.

FIG. 4 depicts a flow chart of a preferred process implemented by thepresent invention to detect pulses on a telephone line with time domaincharacteristics consistent with a three-way call click.

FIG. 5 depicts a flow chart of a preferred process implemented by thepresent invention to calculate and analyze the phases of the frequencycomponents that comprise a pulse.

FIG. 6 depicts a graphical representation of how the output of the FFTis used to calculate a phase for each component of a pulse.

FIG. 7 shows a block diagram of an alternate configuration of thethree-way call detection system of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As required, a detailed illustrative embodiment of the present inventionis disclosed herein. However, techniques, systems and operatingstructures in accordance with the present invention may be embodied in awide variety of forms and modes, some of which may be quite differentfrom those in the disclosed embodiment. Consequently, the specificstructural and functional details disclosed herein are merelyrepresentative, yet in that regard, they are deemed to afford the bestembodiment for purposes of disclosure and to provide a basis for theclaims herein, which define the scope of the present invention. Thefollowing presents a detailed description of the preferred embodiment ofthe present invention.

Referring first to FIG. 1, depicted is three-way call detection circuit101 of the present invention configured to monitor telephone callsbetween an inmate or resident (calling from inmate telephone 103) and acalled party (from called party telephone 111) in telecommunicationssystem 100. In this configuration, inmate telephone 103 connects totelephone network 105 through connection 102, and called party telephone111 connects to telephone network 109 through connection 110. Telephonenetwork 105 and telephone network 109 bi-directionally communicate audiodata through connection 107 thus enabling an inmate or resident atinmate telephone 103 to communicate with a called party at called partytelephone 111.

Three-way call detection circuit 101 monitors connection 107 throughinterface 113. Specifically, interface 113 receives audio signals fromconnection 107 through monitor connection 112. In turn, interface 113provides the signals to three-way call detection circuit 101 throughinterface connection 114. Alternatively, three-way call detectioncircuit 101 can receive data directly from connection 107.

In an alternative configuration, three-way call detection circuit 101can monitor connection 102 between inmate telephone 103 and telephonenetwork 105. If, for example, inmate telephone 103 is in an institutionsuch as a prison, nursing home, school, detention center, hospital,etc., this enables three-way call detection circuit 101 to be internalto the institution.

Three-way call detection circuit 101 (discussed in more detail belowwith respect to FIG. 2) monitors connection 107 (or alternatively,connection 102) for signals indicative of a three-way call attempt.Three-way call detection circuit 101 also communicates with hostcomputer 115 via host connection 116 to inform host computer 115 if athree-way call attempt was initiated by a called party at called partytelephone 111. As discussed earlier, a three-way call is typicallyinitiated when the called party depresses the hook switch on thetelephone, generating a hook-flash signal. The calling party (i.e., theinmate or resident) is temporarily disconnected from the called partywhile the called party establishes a connection with a third party.Then, all three parties can converse.

Three-way call detection circuit 101 is compatible with institutionaltelecommunications systems such as those in prisons, nursing homes,mental institutions, etc. Therefore, host computer 115 may be anycomputer in a telecommunications system, including a host computer inone of the institutions listed above. In these types of institutions itis important to monitor all telephone calls for the presence ofthree-way call attempts to prevent, among other things, inmates orresidents from accessing blocked or restricted telephone numbers. Ifthree-way call detection circuit 101 detects a signal indicative of athree-way call attempt, it communicates this to host computer 115. Hostcomputer 115 can then use this information to take the appropriateaction, which may include disconnecting the telephone call, warning thecalling or the called party, monitoring the call, logging the call,flagging the call, etc.

Turning next to FIG. 2, depicted is a block diagram of the preferredembodiment of three-way call detection circuit 101. As shown, three-waycall detection circuit includes analog to digital (A/D) converter 201,microprocessor 203, digital signal processor 205, energy detectioncircuit 206, memory 207, host port 209, and interface port 211.

During operation, three-way call detection circuit 101 monitors thetelephone line communication between an inmate or resident and a calledparty by receiving audio data from interface 113 through connection 114(see FIG. 1). The system of the present invention is preferablycompatible with both analog and digital telecommunications systems.Therefore, signals received by three-way call detection circuit 101 frominterface 113 may be either analog or digital. If the signals areanalog, A/D converter 201 first converts the signals to a digital formatbefore being sent to microprocessor 203 and digital signal processor205. If the telecommunications system is digital, a D/A converter may beused to transmit analog signals to energy detection circuit 206.Notably, three-way call detection circuit 101 is compatible with asignal represented by 8-bit signed linear data, 8-bit μ-law, 16-bitlinear data, etc.

Signals from connection 114 are received at interface port 211 andtransmitted to both A/D converter 201 and energy detection circuit 206.A/D converter 201 converts analog telephone line data to a digitalsignal compatible with microprocessor 203 and digital signal processor205. As will be discussed with respect to FIG. 3, microprocessor 203instructs digital signal processor 205 and energy detection circuit 206to analyze certain portions of the signal received from the telephoneconnection. Microprocessor 203 uses this analysis to detect signals fromthe telephone line indicative of a three-way call using the algorithm tobe discussed below. If a three-way call attempt is detected,microprocessor 203 informs host computer 115 by transmitting a messageto host port 209. Host port 209, in turn, communicates this messagethrough connection 116 to host computer 115.

To detect a three-way call, three-way call detection circuit 101monitors for pulses of energy with amplitude and phase consistent with athree-way call click. Preferably, the monitoring analyzes signals fromconnection 107 in the time-domain and the frequency domain, where theFFT is used to convert the signal into the frequency domain. The systempreferably first analyzes signals from connection 107 in the time-domainto isolate only those signals with time-domain characteristicsconsistent with a three-way call click. Then, the FFT is performed onsignal samples isolated by this process. This avoids computing thecomputationally intensive FFT for all signal samples received fromconnection 107.

Referring next to FIG. 3 shown is a block diagram of energy detectioncircuit 206 used by three-way call detection circuit 101 to detect anenergy pulse (steps 311 and 313). As shown, energy detection circuit 206preferably comprises audio input 301, isolation transformer 303,sensitivity adjustment circuit 305, amplifier 307, peak detector 309,threshold detector 311, and pulse stretcher 313. Of course, other knowncircuits for detecting energy may be used. In the preferred embodiment,isolation transformer 303 is used to isolate energy detection circuit206 from the circuit of the inmate's or resident's telephone handsetwhile transferring the handset signals from audio input 301 to energydetection circuit 206. This transferred signal is then adjusted bysensitivity adjustment circuit 305 under control of microprocessor 203via sensitivity adjustment line 315. The conditioned signal is thenamplified by amplifier 307.

Peak detector 309 isolates energy pulses in the filtered signal thatexceed a predetermined magnitude. In the preferred embodiment, thepredetermined magnitude is approximately 6 Decibels (dBs), althoughother magnitudes may be chosen in accordance with the invention. Whensuch a pulse is detected, the output of peak detector 309 is driven highand a signal is sent to threshold detector 311, which is comprised ofoperational amplifier 308, and resistors 310 and 312. Preferablyresistors 310 and 312 are both 10 kΩ resistors. If a pulse is providedto threshold detector 311, it passes the signal to pulse stretcher 313.If no pulse is detected, threshold detector 311 does not output thereceived signal.

Preferably, pulse stretcher 313 is used to maintain the output ofthreshold detector 311 at its high level for 20 milliseconds. However,pulse stretcher 313 may be configured to maintain the output ofthreshold detector 311 for any time period. The stretched signal is thenoutput on energy detect line 317 and analyzed by microprocessor 203 todetermine if an energy pulse consistent with a three-way call click hasbeen found (i.e., if the pulse has a magnitude of approximately 6 dBs orgreater).

Referring next to FIG. 4, shown is a flow chart of the method to isolateportions of the signal with time-domain characteristics indicative of athree-way call click. The method is preferably implemented bymicroprocessor 203 in conjunction with digital signal processor 205and/or energy detection circuit 206. The process begins withinitialization step 401. The three-way call detect system of the presentinvention is capable of monitoring all lines of telecommunications in asystem. During initialization step 401, the method begins to receivesignals from each of these telephone lines. Herein, the remainder of thediscussion focuses on the method for monitoring one telephone line.However, the same method can be implemented to monitor all lines ofcommunication simultaneously.

According to the preferred embodiment of the invention, a pulse hastime-domain characteristics consistent with a three-way call click if itis a pulse of energy less than approximately 40 ms in duration and if itis preceded and followed by a period of silence (POS), where each POS isat least approximately 100 ms in duration. Thus, after initializationstep 401, the process monitors the telephone line for a first POS (step403). According to the present invention, silence is a period of timeduring which the signal does not exceed a predefined amplitude. A pulseof energy is a period of time during which the signal does not dropbelow a predefined amplitude.

Preferably a timer is used to measure how long the signal remainssilent. Step 403 begins by setting this timer to zero and then receivinga signal from connection 107 for a predefined sample length. If thesample signal comprises silence, the system increments the timer by thesample-length and checks to see if the time has exceeded 100 ms (step405). If it has not, connection 107 is monitored for anothersample-length of signal (step 403). This process continues until either(1) the line has been silent for longer than 100 ms, or (2) the silenceis broken. If the silence is broken, a check is made that the timer didnot exceed 100 ms and the timer is reset (step 409). If connection 107was not silent for 100 ms or longer, the signal does not contain a POSindicative of a three-way call click, and the process returns to step403.

If however, the timer has reached or exceeded 100 ms, then a POS hasbeen detected. The system next monitors for a pulse of energy with aduration of less than or equal to approximately 40 ms (step 411). Instep 411, an energy timer is set to zero. Once energy is detected instep 413, the timer is incremented (step 415). Next, a check is made tosee if the timer has exceeded 40 ms (step 416). If the timer hasexceeded 40 ms, the system determines that the pulse of energy is notindicative of a three-way call attempt and resets all timers and againreturns to step 403, where telephone line 107 is monitored for a newPOS.

If energy is no longer detected in step 313, the system checks if theduration of the energy pulse was for 40 ms or less (step 417). If thepulse exceeds 40 ms in duration, the system resets all timers and againreturns to step 403. If the pulse is less than 40 ms, the system nextmonitors for another POS following the pulse of energy (step 419). Theprocess for monitoring for a second POS preferably mirrors the processused to monitor for the first POS. Specifically, the system monitors forsilence (step 419) until the timer reaches 100 ms (step 423) or untilsilence is broken. If silence is broken, the timer is reset (step 421).If silence is broken before the timer reaches 100 ms, then the systemdetermines that the signal is not indicative of a three-way call attemptand the process returns to step 403. If, as determined in step 423, theenergy pulse is followed by a POS greater than or equal to 100 ms, thenthe system saves the signal representing the pulse for further analysis.Specifically, as will be discussed with respect to FIG. 5, the processnext isolates the pulse to analyze its components.

As demonstrated in FIG. 5, if a pulse is found with time domaincharacteristics consistent with a three-way telephone call, it is nextanalyzed in the frequency domain to determine if the phase delays of thefrequency components that comprise the pulse are approximately the same.If a sample signal is isolated by the process illustrated in FIG. 3(i.e., it has time-domain characteristics consistent with a three-waycall click), then the process, shown in FIG. 5, first locates data thatrepresents the pulse (step 501). Next, that data is moved to memory 207(step 503). Then, the FFT of the data is calculated and the result isstored in memory 207 (step 505).

Preferably, the signal being analyzed is 8 KHz pulse code modulation(PCM) data. However, the system is compatible with any type of data,including signed linear data, 8-bit μ-law data, 16-bit linear data,analog data, etc. As discussed above, if three-way call detectioncircuit 101 is used to monitor analog connections, A/D converter 201converts the signal to a digital format compatible with digital signalprocessor 205.

For purposes of discussion, it will be assumed that 8 KHz PCM data isused. The FFT is set to compute 512 samples thus resulting in eachsample representing a range of 15.625 Hz. There are many known softwareand hardware modules for computing the FFT of a digital signal. Forexample, computer programming code for computing the FFT is availablefrom the Massachusetts Institute of Technology (MIT) or from other knownsources, such as the Internet. In the preferred embodiment, the FFT iscalculated by digital signal processor 205, although microprocessor 203,a general purpose CPU, a software module, etc., may also be used.

The results of the FFT are stored in memory 207. For a discrete (i.e.,digital) signal, x[t], with N samples, the resulting output is X[w_(k)],where X[w_(k)] is defined as:

$\begin{matrix}{{{X\left\lbrack w_{k} \right\rbrack} = {\sum\limits_{n = 0}^{N - 1}{{x\left\lbrack t_{n} \right\rbrack}{\mathbb{e}}^{{- j}\; w_{k}t_{n}}}}},{k = 0},1,2,\ldots\mspace{11mu},{N - 1}} & (8)\end{matrix}$

In equation 8, x[t_(n)] is the signal in the time domain, t_(n) is then_(th) sampling instant, W_(k) is the k_(th) frequency sample (i.e., thek_(th) frequency component), and X[w_(k)] is the FFT of the signal. TheFFT computes a complex coefficient for each component that comprises thesignal. As discussed earlier, this complex coefficient can be used tocalculate a magnitude and a phase for the component.

In step 507, the phase for each component that comprises the signal,regardless of its magnitude, is calculated and stored in memory 207. Thephase is the arctangent of the imaginary component of the complexcoefficient divided by the real component of the complex coefficient:Phase=atan(Imaginary/Real)  (9)

Therefore, a cosine wave corresponds to a wave with 0 degrees phase (0radians) and a sine wave corresponds to a wave with 90 degrees phase(π/2 radians). The range of possible phase values extends from −180degrees (−π radians) to 180 degrees (π radians).

FIG. 6 shows a graphical representation of how the phase, angle Σ 601,is calculated for a component with coefficient z 603. As can be seen, zis plotted on the complex plane with real axis 605 and imaginary axis607. In this example, z 603 has real component x 609 and imaginarycomponent y 611, and thus is equal to x+jy. Using basic geometry andtrigonometry, it is clear that the phase of angle Σ 601 is the inversetangent of the imaginary component y 611 divided by the relay componentx 609:Σ=arctan(y/x)  (10).

Thus, using this calculation, the phase for each component can becalculated. The resulting calculated phases are stored in memory 207.

Returning to FIG. 5, once the phases for each component of the pulse arecomputed, the phase data is analyzed to determine if the sample includesa click indicative of a three-way call attempt. First, the phases areunwrapped (step 509). As discussed earlier, the FFT calculates amplitudeand a phase for each component that comprises the pulse. However,because of the sinusoidal nature of the output of the FFT, thecalculated phase ranges only from −π to π. If the real phase extendsbeyond this range, large jumps in phase may appear to exist betweencomponents because the calculated phase “wraps around” the −π to πrange. Therefore, phase unwrapping operates to correct thesephase-jumping artifacts by adding multiples of +/−2π when absolute jumpsbetween consecutive phases are greater than a predefined tolerance(e.g., π). The resulting unwrapped phase is devoid of the artificialjumps in phase and is stored in memory 207. Notably, more complex phaseunwrapping techniques are also known, any of which are compatible withthree-way call detection circuit 101.

Next, the characteristics of the unwrapped phase are analyzed forlinearity (step 511). As discussed earlier, phase is in a unit ofradians. However, the system of the present invention is used to locatepulses of energy where each pulse has the same phase delay, which is inunit time. For a component having frequency ω, phase delay, P(ω), isdefined as:P(ω)=Σ(ω)/ω,  (11)where ω is the frequency, and Σ(ω) is the phase, or unwrapped phase.

According to the system of the present invention, if the phase delay ofeach component that comprises a pulse is the same, then the pulse isindicative of a three-way call click. A click is generated by thecentral office and is composed of many frequency components. Because itis a “machine generated” pulse, all of the components are generated atthe same time and should therefore have a common phase delay.

As an alternative to computing the phase delay for each component, thesystem can analyze the phases, or unwrapped phases for linearity. If thephase is linear with respect to frequency (i.e., Σ(ω)=α(ω), where α is aconstant), then through simple mathematical substitution, it is evidentthat the phase delay will be the same (α), independent of ω. Forexample,P(ω)=α*ω/ω  (12)P(ω)=α  (13)

In the art of signal analysis, a group delay, G(ω), is defined as thederivative of the phase and can be used to compute the linearity of thephase as a function of frequency. Group delay, G(ω), is defined as:G(ω)=−d/dω(Σ(ω)).  (14)If the group delay, G(ω), is a constant (i.e., Σ(ω) is linear), then thegroup delay, G(ω), equals the phase delay (i.e., it is α). Thus,preferably, step 511 entails analyzing the group delay of the unwrappedphases of the components that comprise the pulse. If the group delay,G(ω), is a constant, the pulse has frequency components with a commonphase delay and thus is indicative of a three-way call click. Three-waycall detection circuit 101 communicates this to host computer 115, whereappropriate action can be taken (step 513). Such action, as discussedabove, might include monitoring the telephone call, providing a promptthat warns the called party and/or calling party, recording thetelephone call, blocking the telephone call, blocking all futuretelephone calls to that telephone number, flagging the call, etc. If thesystem disconnects the telephone call in step 513, then the processreturns to initialization step 301 (see FIG. 3) where the system beginsmonitoring any new telephone calls. Alternatively, if the three-way callalgorithm allows the telephone call to proceed, then the process resetsall timers and returns to step 303 where the same call is monitored forsubsequent three-way call attempts.

According to the present invention, the system may also use othertechniques to verify that the pulse being analyzed is characteristic ofa three-way call click. These techniques further decrease thepossibility of a false-positive (i.e., the system incorrectlyidentifying a pulse as a three-way call click) by filtering out sampleswith characteristics not indicative of a click.

Referring lastly to FIG. 7, shown is an alternate configuration of thethree-way call detection circuit 101 as used in an institution telephonemanagement system 701. A plurality of user telephones 702, wherein theactual number of telephones depends on the desired capacity of theinstitution call system, are incorporated into a telephone bank 703 andare connected to an electronic switchboard device 705. It is preferredthat telephone bank 703 may be centrally located within a facility toallow for centralized monitoring. However, it is foreseeable thattelephone bank 703 may be located at a multitude of locations internalor external to a facility to allow for efficient monitoring. Each usertelephone 702 may be equipped with biometric sensing device 709, such asa retinal scanner, fingerprint reader, etc., or any combination ofbiometric devices, so that the acquired biometric data can be used foruser authentication. Alternatively, for efficiency, a single biometricsensing device 109 may be employed for a multitude of user telephones102. Additionally, each telephone may incorporate RF receiver 707 and RFtransmitter 708 to provide RF signals for authentication purposes. Inthis scenario, it is foreseeable that each user is be required to wearan RF transmitter 708 device to transmit radio waves to the RF receiver707. RF receiver 707 may be integral to telephone bank 703 or remote totelephone bank 703. Each RF transmitter 708 may be uniquely encoded to aspecific authorized user. The encoded signal for RF transmitter 708 maybe altered on an intermittent basis depending on the security desired atthe institution. RF transmitter 708 may be incorporated into awristband, ankle band, or any other like device. It is foreseeable thatRF transmitter 708 may be semi-permanently or permanently attached to auser's person in any manner.

Electronic switchboard device 705 regulates calls and connects them tothe proper outgoing trunk line 711. Trunk line 711 may consist of amultitude of connections to any number of local, long distance, orinternational telephone service providers. The number of trunk lines 711depends on the outgoing capacity desired by the institution. Inaddition, trunk lines 711 may be analog, digital, or any other type oftrunk lines not yet contemplated. Electronic switchboard device 705further incorporates an integrated channel bank, allowing calls to beprocessed over either analog or digital trunks as required by thetelephone call system 701. Specifically, when one trunk line 711 isoccupied and handling an outgoing communication, electronic switchboarddevice 705 automatically accesses an alternate trunk line 711 to handlethe outgoing communication. If all trunk lines 711 on the system are inuse, the call may be routed to an alternate system (not depicted). Forexample, electronic switchboard device 705 may be interconnected to amultitude of switchboards to allow for expansion of the system to meetthe capacity desired by the institution. A cross point switch integratedinto electronic switchboard device 705 may also accomplish this routing.

Multiple processors may also be incorporated into the architecture. Thisallows call processing even after parallel component failure. Thearchitecture also provides for a sharing of the load between processors,which eliminates system overload during extremely busy periods. Themultiple processors enable the system to handle large volumes of callsat any time, and ensure system integration.

Additionally, electronic switchboard device 705 performs the voiceprompts heard by the calling party and the recipient of the callallowing the parties to respond to the menu selections. Electronicswitchboard device 705 tests outgoing trunk lines as calls are placedand digitizes telephone audio for recording and/or biometric voiceidentification purposes. If no dial tone is present, one of trunk lines711 may be taken out of service for a pre-programmed amount of time formaintenance. These capabilities are pre-programmed into the device'sfirmware. However, it is foreseeable that software and software upgradesmay provide these services in addition to other services useful in thepresent invention.

A central site server 713 interfaces within the telephone call system701 via a first serial port 715. In the preferred embodiment of thepresent invention, an RS-232 serial port is employed for theinterference connection. However, it is foreseeable that other types ofserial ports 715 commonly known in the art may be utilized. Serial port715 may also be comprised of a direct hardware connection or may consistof a series of ports and connecting means commonly known in the art forconnecting electronic devices. Serial port 715 is designed to allowfirmware driven systems, such as electronic switchboard device 705, tointerface with software-based systems, such as a PC designed systemoperating as a site server. All inmate and call information is routedthrough central site server 713. At central site server 713, user callinformation is digitized for efficient data transfer and efficientrecord keeping. Central site server 713 stores at least each user'sfinancial transaction data. It is preferred that central site server 713also stores the digitized audio used for voice prompts as well as eachuser's call restrictions, PIN, biometric verification data, etc.However, depending on the memory requirements, numerous site servers maybe employed. It is foreseeable that older archived data may also bestored on an integral or a remote computer system database (not shown)or kept on additional storage devices on the central site server 713.

Three-way call detection circuit 101 is utilized each time a telephonecall is placed utilizing telephone call system 701. Three-way calldetection circuit 101 is connected to telephone bank 703 and constantlymonitors all active trunk lines 711 and telephone conversations. Duringa telephone call, three-way call detection circuit 101 monitors theconnection and looks for pulses with phase characteristics indicative ofa three-way call, as discussed above. If such a pulse is found, then athree-way event (TWE) is set and three-way call detection circuit 101executes the appropriate response. For example, the TWE may directtelephone call system 701 to disconnect the telephone call, flag thetelephone call, record the telephone call, monitor the telephone call,etc.

While the present invention has been described with reference to thepreferred embodiment and several alternative embodiments, whichembodiments have been set forth in considerable detail for the purposesof making a complete disclosure of the invention, such embodiments aremerely exemplary and are not intended to be limiting or represent anexhaustive enumeration of all aspects of the invention. The scope of theinvention, therefore, shall be defined solely by the following claims.Further, it will be apparent to those of skill in the art that numerouschanges may be made in such details without departing from the spiritand the principles of the invention. It should be appreciated that thepresent invention is capable of being embodied in other forms withoutdeparting from its essential characteristics.

1. A method, comprising: monitoring an audio signal on a telephone line with a detector and detecting an energy pulse in the audio signal on the telephone line, wherein the telephone line is connected to a telephone network of or associated with an institution, a person, or an entity; processing the energy pulse with a processor, wherein the energy pulse comprises a plurality of frequency components; determining a length of the energy pulse on the telephone line; calculating a phase for each of the plurality of frequency components to generate a plurality of phase values; generating a signal if the plurality of phase values are linear and if the length of the energy pulse is less than 40 milliseconds, wherein the signal is indicative that the plurality of phase values are linear and that the length of the energy pulse is less than 40 milliseconds, and further wherein the signal is indicative of a three-way call attempt on the telephone line; and transmitting the signal to a host computer.
 2. The method of claim 1, further comprising: calculating a Fast Fourier Transform of the energy pulse to produce a complex coefficient for each of the plurality of frequency components.
 3. The method of claim 1, further comprising: calculating a phase delay for each of the plurality of frequency components.
 4. The method of claim 1, further comprising: calculating an unwrapped phase for each of the plurality of frequency components.
 5. The method of claim 1, further comprising: calculating a group delay for each of the plurality of frequency components.
 6. The method of claim 1, wherein a duration of the energy pulse is less than 40 milliseconds.
 7. The method of claim 1, wherein a duration of the energy pulse is approximately 40 milliseconds.
 8. The method of claim 1, further comprising: monitoring the telephone line to detect a first period of silence, wherein the first period of silence has a duration lasting at least approximately 100 milliseconds.
 9. The method of claim 8, further comprising monitoring the telephone line to detect a second period of silence, wherein the second period of silence has a duration lasting at least approximately 100 milliseconds.
 10. The method of claim 9, wherein the first period of silence precedes the detecting of the energy pulse and the second period of silence follows the detecting of the energy pulse.
 11. The method of claim 1, wherein the energy pulse exceeds a predetermined amplitude.
 12. The method of claim 1, wherein an amplitude of the energy pulse has a value that exceeds a normalized silence audio level.
 13. The method of claim 1, further comprising monitoring a telephone call on the telephone line.
 14. The method of claim 1, further comprising providing a prompt on the telephone line to warn a called party or a calling party that the three-way call attempt is detected.
 15. The method of claim 1, further comprising recording a telephone call on the telephone line.
 16. The method of claim 1, further comprising blocking a telephone call on the telephone line.
 17. The method of claim 1, further comprising blocking a future call or blocking future calls to a telephone number associated with a called party called via the telephone line.
 18. The method of claim 1, further comprising flagging a telephone call on the telephone line.
 19. The method of claim 1, further comprising disconnecting a telephone call on the telephone line.
 20. A method, comprising: monitoring a telephone line with a detector to detect a first period of silence in an audio signal on the telephone line, wherein the telephone line is connected to a telephone network of or associated with an institution, a person, or an entity; monitoring the telephone line with the detector to detect an energy pulse, wherein the first period of silence is detected prior to detecting the energy pulse; monitoring the telephone line with the detector to detect a second period of silence, wherein the first period of silence precedes the detecting of the energy pulse and the second period of silence follows the detecting of the energy pulse; determining a length of the energy pulse on the telephone line; storing the energy pulse as a pulse Code modulation digital signal; processing the digital signal with a processor; generating phase values for a plurality of components of the digital signal; unwrapping the phase values to produce unwrapped phase data; determining a group delay of the unwrapped phase data; and generating a signal if the group delay is a constant and if the length of the energy pulse is less than 40 milliseconds, wherein the signal is indicative that the group delay is constant and indicative that the length of the energy pulse is less than 40 milliseconds, and further wherein the signal is indicative of a three-way call attempt on the telephone line; and transmitting the signal to a host computer.
 21. The method of claim 20, further comprising: calculating a Fourier Transform of the plurality of components of the digital signal to produce a complex coefficient for each of the plurality of components.
 22. The method of claim 20, wherein a duration of the energy pulse is less than 40 milliseconds.
 23. The method of claim 20, wherein a duration of the energy pulse is approximately 40 milliseconds.
 24. The method of claim 20, wherein the first period of silence has a duration lasting at least approximately 100 milliseconds.
 25. The method of claim 24, wherein the second period of silence has a duration lasting at least approximately 100 milliseconds.
 26. The method of claim 20, wherein an amplitude of the energy pulse has a value that exceeds a normalized silence audio level.
 27. The method of claim 20, wherein the energy pulse exceeds a predetermined amplitude, and wherein the predetermined amplitude is at least approximately 6 Decibels.
 28. The method of claim 20, further comprising providing a prompt on the telephone line to warn a called party or a calling party that the three-way call attempt is detected.
 29. The method of claim 20, further comprising recording a telephone call on the telephone line.
 30. The method of claim 20, further comprising blocking a telephone call on the telephone line.
 31. The method of claim 20, further comprising blocking a future call or blocking future calls to a telephone number associated with a called party called via the telephone line.
 32. The method of claim 20, further comprising flagging a telephone call on the telephone line.
 33. The method of claim 20, further comprising disconnecting a telephone call on the telephone line.
 34. An apparatus, comprising: a detector, wherein the detector monitors a telephone line and detects an energy pulse in an audio signal on the telephone line, and further wherein the telephone line is connected to a telephone network of or associated with an institution, a person, or an entity; a processor, wherein the processor processes the energy pulse, and wherein the processor determines a length of the energy pulse, wherein the energy pulse comprises a plurality of frequency components, and further wherein the processor calculates a phase for each of the plurality of frequency components to generate a plurality of phase values, and further wherein, the processor generates a signal if the plurality of phase values are linear and if the length of the energy pulse is less than 40 milliseconds, wherein the signal is indicative that the plurality of phase values are linear and that the length of the energy pulse is less than 40 milliseconds, and further wherein the signal is indicative of a three-way call attempt on the telephone line; and a transmitter, wherein the transmitter transmits the signal to a host computer.
 35. The apparatus of claim 34, wherein the apparatus calculates a Fast Fourier Transform of the energy pulse to produce a complex coefficient for each of the plurality of frequency components.
 36. The apparatus of claim 34, wherein the apparatus calculates a phase delay for each of the plurality of frequency components.
 37. The apparatus of claim 34, wherein the apparatus calculates an unwrapped phase for each of the plurality of frequency components.
 38. The apparatus of claim 34, wherein the apparatus calculates a group delay for each of the plurality of frequency components.
 39. The apparatus of claim 34, wherein a duration of the energy pulse is less than 40 milliseconds.
 40. The apparatus of claim 34, wherein a duration of the energy pulse is approximately 40 milliseconds.
 41. The apparatus of claim 34, wherein the apparatus monitors the telephone line to detect a first period of silence, wherein the first period of silence has a duration lasting at least approximately 100 milliseconds.
 42. The apparatus of claim 41, wherein the apparatus monitors the telephone line to detect a second period of silence, wherein the second period of silence has a duration lasting at least approximately 100 milliseconds.
 43. The apparatus of claim 42, wherein the first period of silence precedes the detecting of the energy pulse and the second period of silence follows the detecting of the energy pulse.
 44. The apparatus of claim 34, wherein an amplitude of the energy pulse has a value that exceeds a predetermined normalized silence audio level.
 45. The apparatus of claim 34, wherein the apparatus monitors a telephone call on the telephone line.
 46. The apparatus of claim 34, wherein the apparatus provides a prompt on the telephone line to warn a called party or a calling party that the three-way call attempt is detected.
 47. The apparatus of claim 34, wherein the apparatus blocks a telephone call on the telephone line.
 48. The apparatus of claim 34, wherein the apparatus blocks a future call or blocking future calls to a telephone number associated with a called party called via the telephone line.
 49. The apparatus of claim 34, wherein the apparatus flags a telephone call on the telephone line.
 50. The apparatus of claim 34, wherein the apparatus disconnects a telephone call on the telephone line.
 51. An apparatus, comprising: a detector, wherein the detector circuit monitors a telephone line to detect a first period of silence in an audio signal on the telephone line, to detect an energy pulse in the audio signal, and to detect a second period of silence, wherein the telephone line is connected to a telephone network, and further wherein the first period of silence is detected prior to detecting the energy pulse, and further wherein the first period of silence precedes the detecting of the energy pulse and the second period of silence follows the detecting of the energy pulse; a storage device, wherein the storage device stores the energy pulse as a pulse Code modulation digital signal; a processor, wherein the processor determines a length of the energy pulse on the telephone line, and further wherein the processor processes the digital signal, and further wherein the processor generates phase values for a plurality of components of the digital signal, and further wherein the processor unwraps the phase values to produce unwrapped phase data, and further wherein the processor determines a group delay of the unwrapped phase data, and further wherein the processor generates a signal if the group delay is a constant and if the length of the energy pulse is less than 40 milliseconds, wherein the signal is indicative that the group delay is constant and that the length of the energy pulse is less than 40 milliseconds, and further wherein the signal is indicative of a three-way call attempt on the telephone line; and a transmitter, wherein the transmitter transmits the signal to a host computer.
 52. The apparatus of claim 51, wherein the apparatus calculates a Fourier Transform of the plurality of components of the digital signal to produce a complex coefficient for each of the plurality of components.
 53. The apparatus of claim 51, wherein a duration of the energy pulse is less than 40 milliseconds.
 54. The apparatus of claim 51, wherein a duration of the energy pulse is approximately 40 milliseconds.
 55. The apparatus of claim 51, wherein the first period of silence has a duration lasting at least approximately 100 milliseconds.
 56. The apparatus of claim 55, wherein the second period of silence has a duration lasting at least approximately 100 milliseconds.
 57. The apparatus of claim 51, wherein the energy pulse exceeds a predetermined amplitude, wherein the predetermined amplitude is at least approximately 6 Decibels.
 58. The apparatus of claim 51, wherein an amplitude of the energy pulse has a value that exceeds a normalized silence audio level.
 59. The apparatus of claim 51, wherein the apparatus provides a prompt on the telephone line to warn a called party or a calling party that the three-way call attempt is detected.
 60. The apparatus of claim 51, wherein the apparatus records a telephone call on the telephone line.
 61. The apparatus of claim 51, wherein the apparatus blocks a telephone call on the telephone line.
 62. The apparatus of claim 51, wherein the apparatus blocks a future call or blocks future calls to a telephone number associated with a called party called via the telephone line.
 63. The apparatus of claim 51, wherein the apparatus flags a telephone call on the telephone line.
 64. The apparatus of claim 51, wherein the apparatus disconnects a telephone call on the telephone line. 